With the longest British election campaign in full swing, the pollsters are getting more attention than usual. It is disappointing, then, to see a major polling company falling into bad statistical habits.

Certainty

YouGov has conducted a poll of 1800 people that reverses the Conservative lead of a few days ago, which itself reversed Labour’s lead from the previous poll. You might think that the random seeming changes in results separated by only a few days might, indeed, be random sampling errors, but YouGov is happy to imply otherwise with its headline “Labour Lead at 4%”. That headline has been repeated, without any caveats, by The Sunday Times with a banner headline of “Labour races into 4-point lead after Miliband’s TV success”. But it isn’t true. Read More…